Fig. 3 K_a– calibration data for two groups of coarser-textured samples, which consisted of three samples for each group. Best-fit calibration equations, Eq. [5] for the sand-textured soils (dotted line), and Eq. [6] for the gravel soils (dashed line), are also indicated. These groups show dielectric responses that are intermediate between the Topp equation (Eq. [1], lower solid line) and that of the finer ash soils (Eq. [4], upper solid line)